It should be noted that most of the area under the building and courtyards is a 1250-space parking garage. Any trees in the courtyards are likely in big pots above the parking garage.
Each parking space is likely 20 ft by 8 ft, meaning the parking garage is at least 200,000 sq ft (8 x 20 x 1250). This is nearly double the 102,000 square ft of floor space in the Georgia Dome.
For those interested, here is how I created the image. The picture of Isakson Living comes from their promotional materials. Using Google Maps, I compared their image to Google Map images of the area at the 500 ft to an inch scale, and found the Isakson image to be slightly larger. By measuring the distance between the park entrance road and Providence Rd on both images, I found the Isakson Living image was 14% larger than the Google Map 500ft scale map. So, I got the Georgia Dome on Google Maps at 500 ft to an inch, and enlarged it by 14% to match the scale of the Isakson Living image. I rotated the Georgia Dome image 90 degrees, since it actually runs east-west.